A Not-So-Pleasant Surprise: Ochronotic Knee Encountered During Primary Arthroplasty

<b>Background/Objectives:</b> Ochronosis is an uncommon metabolic condition caused by a deficiency of homogentisate 1,2-dioxygenase, leading to the accumulation of homogentisic acid (HGA) in connective tissues. This deposition of HGA in the joints can result in cartilage degeneration and advanced ochronotic arthritis. Although this condition is usually asymptomatic, it can demonstrate devastating articular destruction characterized by dark pigmentation of the tissues. <b>Methods:</b> A 64-year-old female with a medical history consisting of diabetes mellitus type 2, hypertension, and thoracic aortic aneurysm, with no personal or family history of ochronosis or related symptoms, has been diagnosed with progressive knee osteoarthritis, Kellgren and Lawrence grade III, unresponsive to conservative treatment. <b>Results:</b> The patient underwent staged bilateral, bicompartmental, cemented total knee arthroplasty (TKA), during which several pathological changes were incidentally discovered: black-pigmented, weakened articular cartilage and darkened synovial fluid, as well as brittle metaphyseal bone necessitating increased cement application to ensure prosthetic stability. Postoperative recovery was significant for anemia requiring a blood transfusion. Improved knee function was observed in the first month follow-up visit, and the patient was referred for diagnostic confirmation of her condition. <b>Conclusions:</b> This case underscores the importance of recognizing ochronosis as a potential cause of advanced joint degeneration in patients undergoing arthroplasty. Furthermore, the diagnosis might be of clinical relevance, since this case demonstrated postoperative anemia which required blood transfusion. This, combined with the brittleness of bone, highlights the need for meticulous surgical planning and tailored approaches by the unaware surgeon who might encounter such not-so-pleasant findings.